Teleconverters on the new 70-200mm F4 Macro Gii

[bs.shoots]

I'm interested in getting a TC for the lens as it boasts true 1:1 macro with the 2x teleconverter on, and reaching up to 400mm. I have some questions that I hope someone with this combination can help me answer.

What's the image quality like? Does it degrade the image quality (Especially at 400mm)? Should I just NOT use a TC and crop in post? I'm using a 24MP a7ii and that would mean cropping half of that if I want to make it a "2x".
Does it impact the auto focus speed of the lens?
How often do you use this combination?

Keeping in mind that I travel overseas a lot (not going to buy a 400m lens) and am a hobbyist, should I get the 2x TC (for the reach) or the 1.4x TC (for the light)? I see that most users have the 1.4x TC but that's because they aren't using the 70-200mm macro lens and want to have the reach without losing too much light. I also already have a 24-240mm lens (although the image quality isn't the best).

One last question that's unrelated: I've been seeing online "influencers" nowadays saying they do not put a protective filter in front of their lens and that a lens hood is enough to protect it. Claiming that a protective filter will lower their image quality. Is this a load of bull or should I follow their footsteps?
 

[XKAES]

If you want to shoot up to 2X and you want the best quality, you need to get a true macro lens.  These are typically around 50mm and 100mm and go to 1X -- 2X with a converter (but you can use an extension tube instead).  But going past 1X, for the best quality, you should consider an even shorter focal length lens -- to avoid extreme extension or added optics.

Another thing to keep in mind is that in true macro photography, auto-focusing is pretty useless -- unless you are focusing on completely flat objects, like stamps or coins.

Just because a lens is marked "macro" does not mean it gives the best results for macro photos.  It just means it focuses very close -- closer than a "non-macro" lens.  But with a tele-converter or extension tube, you can turn any lens into a "macro" lens.

[bs.shoots]

2 hours ago, XKAES said:

If you want to shoot up to 2X and you want the best quality, you need to get a true macro lens.  These are typically around 50mm and 100mm and go to 1X -- 2X with a converter (but you can use an extension tube instead).  But going past 1X, for the best quality, you should consider an even shorter focal length lens -- to avoid extreme extension or added optics.

Yes I know the lens is only 1:1 with the 2x converter on, I meant using a 2x converter with the lens to achieve 1:1 not going for 2:1 magnification. I also don't intend to get a dedicated macro lens, I'm using my lenses mostly overseas and I want to catch as much different kinds of pictures. I hate the idea of needing to change lens while out and about, I'll change them only back in a clean environment in a hotel.

2 hours ago, XKAES said:

Another thing to keep in mind is that in true macro photography, auto-focusing is pretty useless -- unless you are focusing on completely flat objects, like stamps or coins.

Sorry let me clarify - I intend to use this as my new "all around" lens, so the auto focus will be used for 400mm wildlife/birding.

2 hours ago, XKAES said:

Just because a lens is marked "macro" does not mean it gives the best results for macro photos.  It just means it focuses very close -- closer than a "non-macro" lens.  But with a tele-converter or extension tube, you can turn any lens into a "macro" lens.

Yup, jack of all trades master of none. 

[Pieter]

14 hours ago, bs.shoots said:

I've been seeing online "influencers" nowadays saying they do not put a protective filter in front of their lens and that a lens hood is enough to protect it. Claiming that a protective filter will lower their image quality. Is this a load of bull or should I follow their footsteps?

There's two sides to this story. If you buy good quality multicoated filters, impact on image quality is really insignificant. Buy cheap filters however and your image quality might be completely destroyed, as was the case here:

https://www.lensrentals.com/blog/2017/05/yet-another-post-about-my-issues-with-uv-filters/

The lens hood is a good first line of defense. If your lens falls to the ground, the hood will be shattered, as might the plastic bayonet fitting on your lens, but the optics might be saved. The metal rim of a filter adds another means to dissipate impact energy and to increase the distance between your delicate front lens element and harmful objects. With dedicated protective filters, there's even a (small) chance that the filter glass might stop a direct impact to the front element.

The main reason why I keep filters on all my lenses though is that every time you clean your front element, tiny dust particles cause abrasion on the lens coating and might even scratch the lens surface. If the coating is worn out, the impact on your images will be much larger than any good filter might have caused. A front filter with scratches and worn coating is easily replaced.